ABSTRACT An all-optical switching is realized in a nonlinear photonic crystal made of polystyrene doped with nonlinear optical dye IR140. The operating energy is as low as 0.5 nJ and the response time is about 1 ps.

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We report experimental demonstration of very fast nonlinear response around 1.5 mum in an InP-based two-dimensional photonic crystal. The nonlinearity produced by low pump powers via carrier induced nonlinear refractive index, leads to an efficient wavelength shift of a photonic crystal resonance observed in reflectivity. Thus we show that it is possible to obtain round the clock (rise and recovery) switching times shorter than 10 ps with contrast ratio higher than 80%. (C) 2004 American Institute of Physics.

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We numerically investigate nonlinear propagation of ultrashort pulses in a one-dimensional photonic band gap structure. We find that, near the band edge, nonlinear effects cause a dynamical shift in the location of the band gap. We demonstrate that this nonlinear mechanism can induce intensity-dependent pulse transmission and reflections. In addition, pulse reshaping and pulse generation is observed. This phenomenon has important new applications in both optical limiting and optical switching.

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Transient absorption and emission spectra of IR-140 dye (5,5'-dichloro-11- diphenylamine-3,3'-diethyl-10,12-ethylene-thiatricarbocyanine- perchlorate) in ethanol have been investigated by using the pump supercontinuum-probing technique of 130 fs time resolution. Excited at a wavelength of 807 nm, two peaks at 820 and 840 nm in the emission spectra were observed. The decay of stimulated emission (SE) at 840 nm can be fitted by a dual-exponential function. Meanwhile, a new transient absorption band ranging from 500 to 650 nm was observed and attributed to the transition between the excited singlet states. Its relaxation process could also be fitted by a dual-exponential function. Both relaxation processes of SE and excited-state absorption were probing wavelength-dependent and included a fast relaxation with a decay time of about several picoseconds and a slow relaxation with decay time longer than 0.1 ns. The prime energy structure was proposed according to the relaxation process and transient spectra of IR-140.

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